How many tiles do I need?
Divide the room area by the area of one tile, then add waste. A 12 × 24 in tile is 2 sq ft, so a 120 sq ft room needs 60 tiles before waste and about 66 after 10%.
Waste is not padding — it is cut loss, and it varies by layout more than most people expect. A straight lay wastes about 10%. Running bond wastes 12%. A 45° diagonal wastes 17%, and herringbone can hit 22% because almost every perimeter tile is a compound cut.
Add a full extra box on top for attic stock. Tile is made in dye lots, and a box bought six months later will not match. Repairs after a dropped pan or a plumbing leak are the reason this matters.
How the calculation works
Tile area in square feet = (width in × height in) ÷ 144. Tiles = room area × (1 + waste %) ÷ tile area, rounded up. Boxes = tiles ÷ tiles per box, rounded up.
Thinset coverage assumes a ¼ in square-notch trowel at roughly 95 sq ft per 50 lb bag. Large-format tile needs a ½ in notch and medium-bed mortar, which drops coverage to about 60 sq ft per bag.
Grout quantity depends on joint width, tile size and tile thickness. Narrow joints between large tiles use very little; ⅛ in joints between small mosaics use a lot. The figure here is a planning estimate — check the manufacturer chart for tight budgets.
Typical tile and setting material cost, mid-2026
| Material | Unit | Typical range |
|---|---|---|
| Ceramic tile | per sq ft | $1.50 – $6.00 |
| Porcelain tile | per sq ft | $3.00 – $12.00 |
| Natural stone | per sq ft | $7.00 – $30.00 |
| Thinset mortar | per 50 lb bag | $15.00 – $32.00 |
| Grout | per 25 lb bag | $18.00 – $35.00 |
| Uncoupling membraneCheap insurance over wood subfloors | per sq ft | $1.80 – $3.50 |
| Backer board | per 3×5 sheet | $12.00 – $22.00 |
| Installation labour | per sq ft | $5.00 – $15.00 |
What goes wrong on this job
- Buy one extra box beyond the calculated figure and store it. Dye lots change, patterns get discontinued, and a single cracked tile in year three becomes a whole-floor problem without attic stock.
- Check every box is the same lot number before you start setting. Mixing lots mid-floor produces a visible shade line that no amount of grout will hide.
- Dry-lay the first row before mixing thinset. Where the cut lands at the wall determines whether the room reads as intentional or as an accident, and you only get one chance to shift the layout.
- Large-format tile is unforgiving of floor flatness. A ½ in dip in 10 ft that nobody notices under vinyl will cause lippage and cracked tiles under 24 in porcelain.
- Order tile before demolition starts, not after. Lead times on anything not in stock run 2–6 weeks, and a family living around an unfinished bathroom gets expensive in goodwill.
Frequently asked questions
How much extra tile should I buy?
10% for a straight lay, 15% for diagonal and 20% for herringbone — then one additional box on top for future repairs. Rooms with lots of jogs, niches or angled walls need more.
How many 12x24 tiles in 100 square feet?
Each 12 × 24 tile covers 2 sq ft, so 50 tiles cover 100 sq ft exactly. With 10% waste you need 55, and boxes usually hold 8, so you order 7 boxes.
How much thinset do I need per square foot?
A 50 lb bag covers roughly 95 sq ft with a ¼ in square-notch trowel, or about 60 sq ft with the ½ in notch that large-format tile requires.
Does tile waste depend on room shape?
Heavily. A simple rectangle wastes far less than the same square footage broken up by doorways, closets and angled walls. Add 5% beyond the pattern allowance for a complicated footprint.